compilation.emitAsset is not a function in sitemap-webpack-plugin

I'm trying to build a sitemap in my production environment and I have been trying to use sitemap-webpack-plugin but get the following error:

ERROR in TypeError: compilation.emitAsset is not a function
    at /Users/ME/Sites/test-site/node_modules/sitemap-webpack-plugin/lib/index.js:378:41
    at Array.forEach (<anonymous>)
    at SitemapWebpackPlugin.<anonymous> (/Users/ME/Sites/test-site/node_modules/sitemap-webpack-plugin/lib/index.js:377:34)
    at step (/Users/ME/Sites/test-site/node_modules/sitemap-webpack-plugin/lib/index.js:86:23)
    at Object.next (/Users/ME/Sites/test-site/node_modules/sitemap-webpack-plugin/lib/index.js:67:53)
    at fulfilled (/Users/ME/Sites/test-site/node_modules/sitemap-webpack-plugin/lib/index.js:57:58)

My package.json:

"sitemap-webpack-plugin": "^1.1.0",
"webpack": "4.28.0",

Inside my webpack.prod:

const SitemapPlugin = require('sitemap-webpack-plugin').default;
const paths = ['url/', 'url/url2'];

// later down the file inside plugins:

new SitemapPlugin({ base: 'https://www.bob.com', paths })

As I'm using webpack 4 I thought emitAsset should work?

Has anyone else come across this?